U.S. patent number 8,599,114 [Application Number 12/686,885] was granted by the patent office on 2013-12-03 for pixel and organic light emitting display device using the same.
This patent grant is currently assigned to Samsung Display Co., Ltd.. The grantee listed for this patent is Woong-Sik Choi, Yang-Wan Kim. Invention is credited to Woong-Sik Choi, Yang-Wan Kim.
United States Patent |
8,599,114 |
Kim , et al. |
December 3, 2013 |
Pixel and organic light emitting display device using the same
Abstract
A display device displays an image having a substantially
uniform brightness by compensating for variations of the threshold
voltages of driving transistors and compensating for the
deterioration of an organic light emitting diode. A pixel includes
an organic light emitting diode, two transistors, a storage
capacitor, and a compensation unit. A driving transistor supplies a
current to an OLED corresponding to the voltage in the storage
capacitor. The compensation unit controls a voltage of a gate
electrode of the driving transistor corresponding to a
deterioration of the organic light emitting diode, and couples one
electrode of the driving transistor to the data line during a
compensation period, during which a threshold voltage of the
driving transistor is compensated.
Inventors: |
Kim; Yang-Wan (Yongin,
KR), Choi; Woong-Sik (Yongin, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Yang-Wan
Choi; Woong-Sik |
Yongin
Yongin |
N/A
N/A |
KR
KR |
|
|
Assignee: |
Samsung Display Co., Ltd.
(Yongin-si, KR)
|
Family
ID: |
42040290 |
Appl.
No.: |
12/686,885 |
Filed: |
January 13, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100253608 A1 |
Oct 7, 2010 |
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Foreign Application Priority Data
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Apr 2, 2009 [KR] |
|
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10-2009-0028438 |
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Current U.S.
Class: |
345/76; 345/211;
345/92 |
Current CPC
Class: |
G09G
3/3233 (20130101); G09G 2300/0819 (20130101); G09G
2300/0809 (20130101); G09G 2320/045 (20130101); G09G
2320/0295 (20130101); G09G 2300/0852 (20130101); G09G
2320/043 (20130101) |
Current International
Class: |
G09G
3/30 (20060101); G09G 5/00 (20060101); G09G
3/36 (20060101) |
Field of
Search: |
;345/76-77 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1835058 |
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CN |
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101266757 |
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CN |
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101373578 |
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Feb 2009 |
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CN |
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1 923 857 |
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May 2008 |
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EP |
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2004-252110 |
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Sep 2004 |
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JP |
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2005-189695 |
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Jul 2005 |
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JP |
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2006-38963 |
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Feb 2006 |
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10-2003 0081919 |
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Oct 2003 |
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KR |
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1020050110961 |
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Nov 2005 |
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KR |
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1020060054603 |
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May 2006 |
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KR |
|
100815756 |
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Mar 2008 |
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KR |
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10-0821041 |
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Apr 2008 |
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KR |
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10-0844770 |
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Jul 2008 |
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KR |
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1020080080753 |
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Sep 2008 |
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KR |
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WO 2007/037269 |
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Apr 2007 |
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WO |
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Other References
EPO Office Action and Extended Search Report for corresponding
European Patent Application No. 10155346.9, dated Aug. 5, 2011, 11
pages. cited by applicant .
JPO Office Action dated Jan. 4, 2012, for corresponding Japanese
Patent Application No. 2009-203427, listing the references cited
under "Foreign Patent Documents," 2 pages. cited by applicant .
Chinese Office action dated Mar. 19, 2012 for corresponding Chinese
Patent Application No. 201010115154.7, 8pp. cited by applicant
.
Korean Office Action dated Jul. 7, 2011 for corresponding Korean
priority application No. KR 10-2009-0028438. cited by applicant
.
SIPO Certificate of Patent dated Jan. 13, 2013, for corresponding
Chinese Patent application 201010115154.7, (3 pages). cited by
applicant.
|
Primary Examiner: Mengistu; Amare
Assistant Examiner: Nadkarni; Sarvesh J
Attorney, Agent or Firm: Christie, Parker & Hale,
LLP
Claims
What is claimed is:
1. A pixel comprising: an organic light emitting diode; a first
transistor coupled to a scan line and a data line, the first
transistor configured to be turned on when a scan signal is
supplied to the scan line; a storage capacitor for storing a
voltage corresponding to a data signal supplied to the data line; a
second transistor for supplying a current corresponding to the
voltage stored in the storage capacitor, the current flowing from a
first power supply to a second power supply via the organic light
emitting diode; and a compensation unit for controlling a voltage
of a gate electrode of the second transistor corresponding to a
deterioration of the organic light emitting diode, and for coupling
a first electrode of the second transistor to the data line during
a compensation period in which a threshold voltage of the second
transistor is compensated, wherein the compensation unit comprises:
a fourth transistor and a fifth transistor, the fourth and fifth
transistors being coupled between the first electrode of the second
transistor and the data line; and a third transistor coupled
between a first node and a voltage source, the first node being a
common terminal of the fourth transistor and the fifth
transistor.
2. The pixel as claimed in claim 1, wherein the compensation unit
further comprises: a feedback capacitor coupled between the first
node and the gate electrode of the second transistor.
3. The pixel as claimed in claim 2, wherein a gate electrode of the
fifth transistor is coupled to a control line substantially
parallel to the scan line, such that the fifth transistor is
configured to be turned on during the compensation period.
4. The pixel as claimed in claim 3, wherein a gate electrode of the
fourth transistor is coupled to the scan line and is configured to
be turned on during the compensation period, concurrently with the
fifth transistor.
5. The pixel as claimed in claim 2, wherein a gate electrode of the
third transistor is coupled to an emission control line
substantially parallel to the scan line.
6. The pixel as claimed in claim 5, wherein a turn-on time of the
third transistor does not overlap with a turn-on time of the fourth
transistor during a normal driving period.
7. The pixel as claimed in claim 2, wherein the voltage source has
a higher voltage than a voltage applied to an anode electrode of
the organic light emitting diode.
8. The pixel as claimed in claim 2, wherein the voltage source has
a lower voltage than a voltage applied to an anode electrode of the
organic light emitting diode.
9. The pixel as claimed in claim 8, wherein a voltage of the
voltage source is substantially identical to a voltage of the
second power supply.
10. An organic light emitting display device comprising: a
plurality of scan lines, a plurality of emission control lines, and
a plurality of control lines extending across a display region; a
plurality of data lines extending across the display region and
crossing the scan lines, emission control lines, and control lines;
a plurality of pixels at respective crossings of the scan lines,
emission control lines, control lines, and data lines; a scan
driver for sequentially supplying scan signals to the scan lines
during a compensation period for compensating a threshold voltage
and during a normal driving period, and for sequentially supplying
emission control signals to the emission control lines during the
normal driving period; a control line driver for sequentially
supplying control signals to the control lines during the
compensation period; a data driver for supplying data signals to
the data lines, the data signals corresponding to second data
supplied from a timing controller; a sensing unit for sensing
threshold voltage/mobility information of driving transistors in
respective ones of the pixels; a switching unit for selectively
coupling the sensing unit and/or the data driver to the data lines;
a control block for storing the threshold voltage/mobility
information of the driving transistors sensed by the sensing unit;
and the timing controller for generating the second data in
accordance with first data supplied from an external source
utilizing the threshold voltage/mobility information stored in the
control block, wherein each of the respective pixels comprises an
organic light emitting diode and a compensation unit for coupling a
respective one of the driving transistors to a respective one of
the data lines during the compensation period and for compensating
for a deterioration of the organic light emitting diode during the
normal driving period, wherein the respective one of the driving
transistors is coupled between a first power supply and a second
power supply, and wherein the compensation unit comprises: a fourth
transistor and a fifth transistor, the fourth and fifth transistors
being coupled between a data line of the data lines and the driving
transistor; and a third transistor coupled between a first node and
a voltage source, the first node being a common terminal of the
fourth transistor and the fifth transistor.
11. The organic light emitting display device as claimed in claim
10, wherein the sensing unit comprises: a current sink unit for
sinking a first current from a specific pixel of the pixels via a
specific driving transistor of the driving transistors in the
specific pixel; and an analog-digital converter for converting a
first voltage to a first digital value, the first voltage generated
when the first current is sunken.
12. The organic light emitting display device as claimed in claim
11, wherein the switching unit comprises: a second switching
element between the current sink unit and the data line, the second
switching element configured to be turned on during the
compensation period; and a first switching element between the data
driver and the data line, the first switching element configured to
be turned on during the normal driving period.
13. The organic light emitting display device as claimed in claim
11, wherein the control block comprises: a memory for storing the
first digital value; and a control unit for transferring the first
digital value to the timing controller.
14. The organic light emitting display device as claimed in claim
13, wherein the control unit is configured to transfer the first
digital value generated from the specific pixel to the timing
controller when the first data to be supplied to the specific pixel
is input to the timing controller.
15. The organic light emitting display device as claimed in claim
13, wherein the timing controller is configured to generate the
second data having j bits (j is a natural number greater than i)
based on the first data having i bits (i is a natural number)
utilizing the first digital value to compensate the threshold
voltage/mobility.
16. The organic light emitting display device as claimed in claim
10, wherein during the normal driving period, the scan driver is
configured to supply a first emission control signal of the
emission control signals to a first emission control line of the
emission control lines, the first emission control signal at least
partially overlapping a first scan signal of the scan signals, the
first scan signal supplied to a first scan line of the scan lines
corresponding to the first emission control line, and having a
wider width than a width of the first scan signal.
17. The organic light emitting display device as claimed in claim
16, wherein during the compensation period, the control line driver
is configured to supply a first control signal of the control
signals to a first control line of the control lines concurrently
with a second scan signal of the scan signals supplied to a second
scan line of the scan lines corresponding to the first control
line.
18. The organic light emitting display device as claimed in claim
17, wherein each of the respective pixels further comprises: a
first transistor coupled to a respective scan line of the scan
lines and a respective data line of the data lines, the first
transistor configured to be turned on when a scan signal of the
scan signals is supplied to the respective scan line; a storage
capacitor for storing a voltage corresponding to a data signal of
the data signals supplied to the respective data line; and the
respective one of the driving transistors for supplying a current
corresponding to the voltage stored in the storage capacitor from
the first power supply to the second power supply via the organic
light emitting diode, wherein a voltage of a gate electrode of the
driving transistor is controlled by the compensation unit.
19. The organic light emitting display device as claimed in claim
18, wherein the compensation unit comprises: the fourth transistor
coupled to a first electrode of the driving transistor, the fourth
transistor configured to be turned on when the scan signal is
supplied to the respective scan line; the fifth transistor coupled
between the fourth transistor and the data line, the fourth
transistor configured to be turned on when the control signal is
supplied to the respective control line; the third transistor
coupled between a first node and a voltage source, the first node
being a common terminal of the fourth transistor and the fifth
transistor, the third transistor configured to be turned on when an
emission control signal of the emission control signals is supplied
to a respective emission control line of the emission control
lines; and a feedback capacitor coupled between the first node and
a gate electrode of a second transistor.
20. The organic light emitting display device as claimed in claim
19, wherein the voltage source is configured to supply a higher
voltage than a voltage applied to an anode electrode of the organic
light emitting diode.
21. The organic light emitting display device as claimed in claim
19, wherein the voltage source is configured to supply a lower
voltage than a voltage applied to an anode electrode of the organic
light emitting diode.
22. The organic light emitting display device as claimed in claim
21, wherein the voltage source is configured to supply a voltage
substantially identical to a voltage supplied by the second power
supply.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to and the benefit of Korean
Patent Application No. 10-2009-0028438, filed on Apr. 2, 2009, in
the Korean Intellectual Property Office, the entire content of
which is incorporated herein by reference.
BACKGROUND
1. Field
The present invention relates to a pixel and an organic light
emitting display device using the same.
2. Discussion of Related Art
Recently, various flat panel display devices that are lighter in
weight and smaller in volume than a cathode ray tube, have been
developed. Among the flat panel display devices, there are liquid
crystal display devices, field emission display devices, plasma
display panels, and organic light emitting display devices,
etc.
Among the flat panel display devices, the organic light emitting
display devices display images using organic light emitting diodes
that generate light by a recombination of electrons and holes.
Organic light emitting display devices are driven at low power
consumption, with rapid response speed.
FIG. 1 is a schematic circuit diagram showing a pixel of a
conventional organic light emitting display device.
Referring to FIG. 1, the pixel 4 of the conventional organic light
emitting display device includes an organic light emitting diode
OLED, and a pixel circuit 2 that is coupled to a data line Dm and a
scan line Sn to control the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is
coupled to the pixel circuit 2, and the cathode electrode of the
organic light emitting diode OLED is coupled to a second power
supply ELVSS. The pixel circuit 2 controls the amount of current
supplied to the organic light emitting diode OLED according to the
data signal supplied to the data line Dm when a scan signal
supplied to the scan line Sn. To this end, the pixel circuit 2
includes a second transistor M2 coupled between a first power
supply ELVDD and the organic light emitting diode OLED, a first
transistor M1 coupled between the second transistor M2, the data
line Dm, and the scan line Sn, and a storage capacitor Cst that is
coupled between the gate electrode and a first electrode of the
second transistor M2.
The gate electrode of the first transistor M1 is coupled to the
scan line Sn, and a first electrode of the first transistor M1 is
coupled to the data line Dm. A second electrode of the first
transistor M1 is coupled to one terminal of the storage capacitor
Cst. Here, the first electrode of the first transistor M1 is either
a source electrode or a drain electrode, and the second electrode
is an electrode other than the electrode of the first electrode.
For example, if the first electrode is the source electrode, the
second electrode is the drain electrode. When the scan signal is
supplied to the scan line Sn, the first transistor M1 coupled
between the scan line Sn and the data line Dm is turned on to
supply the data signal supplied from the data line Dm to the
storage capacitor Cst. Thus, the storage capacitor Cst is charged
with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one
terminal of the storage capacitor Cst, and the first electrode is
coupled to the other terminal of the storage capacitor Cst and the
first power supply ELVDD. The second electrode of the second
transistor M2 is coupled to the anode electrode of the organic
light emitting diode OLED. The second transistor M2 controls the
amount of current flowing from the first power supply ELVDD to the
second power supply ELVSS via the organic light emitting diode OLED
in accordance with the voltage stored in the storage capacitor Cst.
Accordingly, the organic light emitting diode OLED generates light
corresponding to the amount of current supplied by the second
transistor M2.
However, an issue with the conventional organic light emitting
display device as described above is that an image having a desired
brightness cannot be displayed due to changes in efficiency
according to the deterioration of the organic light emitting diode
OLED. That is, the organic light emitting diode OLED deteriorates
as time elapses, and accordingly, light having a gradually lowering
brightness is generated corresponding to the same data signal.
Another issue with the conventional organic light emitting display
device is that an image having a uniform brightness cannot be
displayed due to the non-uniformity in threshold voltage/mobility
of the driving transistors M2 included in each pixel 4.
SUMMARY
An aspect of an embodiment of the present invention is directed
toward an organic light emitting display having pixels that display
images having a substantially uniform brightness by compensating
for variations in the threshold voltage of driving transistors
outside the pixels and compensating for the deterioration of
organic light emitting diodes inside the pixels. Another aspect of
an embodiment of the present invention is directed toward a pixel
having a driving transistor and an organic light emitting diode,
where the pixel compensates a threshold voltage/mobility of the
driving transistor, and compensates for the deterioration of the
organic light emitting diode.
According to one embodiment, a pixel includes an organic light
emitting diode, first and second transistors, a storage capacitor,
and a compensation unit. The first transistor is coupled to a scan
line and a data line, and is configured to be turned on when a scan
signal is supplied to the scan line. The storage capacitor stores a
voltage corresponding to a data signal supplied to the data line.
The second transistor supplies a current corresponding to the
voltage stored in the storage capacitor, the current flowing from a
first power supply to a second power supply via the organic light
emitting diode. The compensation unit controls the voltage of a
gate electrode of the second transistor corresponding to a
deterioration of the organic light emitting diode, and couples a
first electrode of the second transistor to the data line during a
compensation period in which a threshold voltage of the second
transistor is compensated.
In one embodiment, the compensation unit includes third through
fifth transistors, and a feedback capacitor. The fourth and fifth
transistors are coupled between the first electrode of the second
transistor and the data line. The third transistor is coupled
between a first node and a voltage source, the first node being a
common terminal of the fourth transistor and the fifth transistor.
The feedback capacitor is coupled between the first node and the
gate electrode of the second transistor. The gate electrode of the
fifth transistor may be coupled to a control line substantially
parallel to the scan line, such that the fifth transistor is
configured to be turned on during the compensation period.
The gate electrode of the fourth transistor may be coupled to the
scan line and is configured to be turned on during the compensation
period concurrently with the fifth transistor. A gate electrode of
the third transistor may be coupled to an emission control line
substantially parallel to the scan line. A turn-on time of the
third transistor does not overlap with a turn-on time of the fourth
transistor during a normal driving period.
According to one embodiment of the present invention, an organic
light emitting display device includes a plurality of scan lines,
emission control lines, and control lines extending across a
display region, and a plurality of data lines extending across the
display region to cross the scan lines, emission control lines, and
control lines. A plurality of pixels are at respective crossings of
the scan lines, emission control lines, and data lines. Further,
the display device includes a scan driver, control line driver,
data driver, a sensing unit, a switching unit, a control block, and
a timing controller. The scan driver sequentially supplies scan
signals to the scan lines during a compensation period for
compensating a threshold voltage and during a normal driving
period, and sequentially supplies emission control signals to the
emission control lines during the normal driving period. The
control line driver sequentially supplies control signals to the
control lines during the compensation period. The data driver
supplies data signals to the data lines, the data signals
corresponding to second data supplied from a timing controller. The
sensing unit senses threshold voltage/mobility information of
driving transistors in respective ones of the pixels. The switching
unit selectively couples the sensing unit and/or the data driver to
the data lines. The control block stores the threshold
voltage/mobility information of the driving transistors sensed by
the sensing unit. The timing controller generates the second data
by in accordance with first data supplied from an external source
utilizing the threshold voltage/mobility information stored in the
control block. Each of the respective pixels includes an organic
light emitting diode and a compensation unit that couples a
respective one of the driving transistors to a respective one of
the data lines during the compensation period and compensates for a
deterioration of the organic light emitting diode during the normal
driving period.
In one embodiment, the sensing unit includes a current sink unit
for sinking a first current from a specific pixel of the pixels via
a specific driving transistor of the driving transistors, and an
analog-digital converter for converting a first voltage to a first
digital value, the first voltage generated when the first current
is sunken.
The switching unit may include a second switching element
positioned between the current sink unit and the data line, the
second switching element configured to be turned on during the
compensation period, and a first switching element positioned
between the data driver and the data line, the first switching
element configured to be turned on during the normal driving
period.
The control block may include a memory for storing the first
digital value, and a control unit for transferring the first
digital value to the timing controller. The control unit may be
configured to transfer the first digital value generated from a
specific pixel of the pixels to the timing controller when the
first data to be supplied to the specific pixel is input to the
timing controller.
The timing controller may be configured to generate the second data
having j bits (j is a natural number greater than i) based on the
first data having i bits (i is a natural number) utilizing the
first digital value to compensate the threshold voltage/mobility.
During the normal driving period, the scan driver may be configured
to supply a first emission control signal of the emission control
signals to a first emission control line of the emission control
lines, the first emission control signal at least partially
overlapping a first scan signal of the scan signals, the first scan
signal supplied to a first scan line of the scan lines
corresponding to the first emission control line, and having a
wider width than a width of the first scan signal. During the
compensation period, the control line driver may be configured to
supply a first control signal of the control signals to a first
control line of the control lines concurrently with a second scan
signal of the scan signals supplied to a second scan line of the
scan lines corresponding to the first control line.
With the pixel and the organic light emitting display device using
the same according to various embodiments of the present invention,
the deviation in the threshold voltages of driving transistors
generated by variations in manufacturing processes is compensated
outside the pixels. Here, the transistors and other components for
compensating for the threshold voltage are not inside the pixel.
Also, in various embodiments of the present invention, a
compensation unit is additionally installed inside each of the
pixels, thus compensating for the deterioration of the organic
light emitting diode and displaying an image having a substantially
uniform brightness accordingly.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, together with the specification,
illustrate exemplary embodiments of the present invention, and,
together with the description, serve to explain the principles of
the present invention.
FIG. 1 is a schematic circuit diagram showing a pixel of a
conventional organic light emitting display device;
FIG. 2 is a schematic block diagram showing an organic light
emitting display device according to an embodiment of the present
invention;
FIG. 3 is a schematic circuit diagram showing an embodiment of the
pixel of FIG. 2;
FIG. 4 is a schematic circuit diagram showing an embodiment of the
compensation unit of FIG. 3;
FIG. 5 is a schematic block diagram showing the switching unit, the
sensing unit, and the control block of FIG. 2;
FIG. 6 is a schematic block diagram showing the data driver of FIG.
2;
FIG. 7 is a schematic block diagram showing a driving waveform
supplied during a compensation period of the threshold voltage and
an operation process; and
FIG. 8 is a schematic block diagram showing a driving waveform
supplied during a normal driving period and an operation
process.
DETAILED DESCRIPTION
In the following detailed description, only certain exemplary
embodiments of the present invention are shown and described, by
way of illustration. As those skilled in the art would recognize,
the invention may be embodied in many different forms and should
not be construed as being limited to the embodiments set forth
herein. Also, in the context of the present application, when an
element is referred to as being "connected" or "coupled" to another
element, it can be directly connected or coupled to the another
element or be indirectly connected or coupled to the another
element with one or more intervening elements interposed
therebetween. Like reference numerals designate like elements
throughout the specification.
Hereinafter, exemplary embodiments of the present invention,
proposed so that a person having ordinary skill in the art can
easily carry out the present invention, will be described in more
detailed with reference to the accompanying FIG. 2 to FIG. 8.
FIG. 2 is a schematic block diagram showing an organic light
emitting display device according to an exemplary embodiment of the
present invention.
Referring to FIG. 2, the organic light emitting display device
according to the exemplary embodiment of the present invention
includes a display region 130 that includes pixels 140 coupled to
scan lines S1 to Sn, emission control lines E1 to En, control lines
CL1 to CLn, and data lines D1 to Dm, a scan driver 110 that drives
the scan lines S1 to Sn and emission control lines E1 to En, a
control line driver 160 that drives the control lines CL1 to CLn, a
data driver 120 that drives the data lines D1 to Dm, and a timing
controller 150 that controls the scan driver 110, the data driver
120, and the control line driver 160.
The organic light emitting display device according to the
exemplary embodiment of the present invention further includes a
sensing unit 180 that extracts threshold voltage/mobility
information of driving transistors included in the respective
pixels 140, a switching unit that selectively couples the sensing
unit 180 and the data driver 120 to the data lines D1 to Dm, and a
control block 190 that stores the information sensed by the sensing
unit 180.
The display region 130 includes the pixels 140 positioned at
crossings of the scan lines S1 to Sn, the emission control lines E1
to En, the control lines CL1 to CLn, and the data lines D1 to Dm.
The pixels 140 receive a first power ELVDD and a second power ELVSS
from an external source. The pixels 140 control an amount of
current supplied from the first power ELVDD to the second power
ELVSS via the organic light emitting diode in accordance with the
data signals. In some embodiments, compensation units (e.g.,
compensation unit 142 of FIG. 3) are installed in each of the
pixels 140 to compensate for the deterioration of the organic light
emitting diode.
The scan driver 110 sequentially supplies the scan signals to the
scan lines S1 to Sn in accordance with the control of the timing
controller 150. Also, the scan driver 110 supplies the emission
control signals to the emission control lines E1 to En in
accordance with the control of the timing controller 150.
The control line driver 160 sequentially supplies the control
signals to the control lines CL1 to CLn in accordance with the
control of the timing controller 150.
The data driver 120 supplies the data signals to the data lines D1
to Dm in accordance with the control of the timing controller
150.
The switching unit 170 selectively couples the sensing unit 180 and
the data driver 120 to the data lines D1 to Dm. To this end, the
switching unit 170 has at least one switching element coupled to
each of the data lines D1 to Dm, respectively (that is, in each
channel).
The sensing unit 180 extracts threshold voltage/mobility
information of driving transistors included in each of the pixels
140, and supplies the extracted threshold voltage/mobility
information to the control block 190. To this end, the sensing unit
180 has a current sink unit (e.g., current sink unit 181 in FIG. 5)
coupled to each of the data lines D1 to Dm, respectively (that is,
in each channel).
The control block 190 stores the threshold voltage/mobility
information supplied by the sensing unit 180. In some embodiments,
the control block 190 stores threshold voltage/mobility information
of driving transistors included in all pixels 140. To this end, the
control block 190 has a memory and a control unit that transfers
the information stored in the memory to the timing controller
150.
The timing controller 150 controls the data driver 120, the scan
driver 110, and the control driver 160. Also, the timing controller
150 generates a second data Data2 by converting a digital value of
a first data Data1 input from an external source corresponding to
the information supplied by the control block 190 so that the
threshold voltage/mobility of the driving transistor is
compensated. Here, the first data Data1 has i bits (i is a natural
number), and the second data Data2 has j bits (j is a natural
number of i or more).
The second data Data2 generated by the timing controller 150 is
supplied to the data driver 120. Then, the data driver 120
generates data signals using the second data Data2, and supplies
the generated data signals to the pixels 140.
FIG. 3 is a schematic circuit diagram showing an exemplary
embodiment of the pixel 140 of FIG. 2. For convenience of
explanation, the pixel 140 coupled to an n.sup.th scan line Sn and
an m.sup.th data line (Dm) will be described in FIG. 3.
Referring to FIG. 3, the pixel 140 according to the embodiment of
the present invention includes a first transistor M1 that is
coupled to an organic light emitting diode OLED, a scan line Sn,
and a data line Dm, a second transistor M2 that controls the amount
of current supplied to the organic light emitting diode OLED
corresponding to the voltage stored in a storage capacitor Cst, and
a compensation unit 142 that selectively couples the second
electrode of the second transistor M2 to the data line Dm and
simultaneously or concurrently compensates for the deterioration of
the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is
coupled to a second electrode of the second transistor M2, and the
cathode electrode of the organic light emitting diode OLED is
coupled to a second power supply ELVSS. The organic light emitting
diode OLED generates light having a brightness (e.g., a
predetermined brightness) corresponding to the amount of current
supplied by the second transistor M2.
A gate electrode of the first transistor M1 is coupled to the scan
line Sn, and a first electrode of the first transistor M1 is
coupled to the data line Dm. A second electrode of the first
transistor M1 is coupled to a gate electrode of the second
transistor M2 (a driving transistor). Thus, the first transistor M1
supplies the data signal from the data line Dm to the gate
electrode of the second transistor M2 when the scan signal is
supplied to the scan line.
The gate electrode of the second transistor M2 is coupled to the
second electrode of the first transistor M1, and a first electrode
of the second transistor M2 is coupled to a first power supply
ELVDD. The second electrode of the second transistor M2 is coupled
to the anode electrode of the organic light emitting diode OLED.
The second transistor M2 controls the amount of current flowing
from the first power supply ELVDD to the second power supply ELVSS
via the organic light emitting diode OLED, the amount of current
corresponding to the voltage applied to the gate electrode of the
second transistor M2. To this end, the voltage of the first power
supply ELVDD is set to be higher than the voltage of the second
power supply ELVSS.
One terminal of the storage capacitor Cst is coupled to the gate
electrode of the second transistor M2, and the other terminal of
the storage capacitor Cst is coupled to the first power supply
ELVDD. The storage capacitor Cst is charged with (e.g., stores) a
voltage corresponding to the data signal when the first transistor
M1 is turned on.
The compensation unit 142 controls the voltage of the gate
electrode of the second transistor M2 corresponding to the
deterioration of the organic light emitting diode OLED. In other
words, the compensation unit 142 controls the voltage of the gate
electrode of the second transistor M2 to compensate for the
deterioration of the organic light emitting diode OLED. The
compensation unit 142 couples the data line Dm to the second
electrode of the second transistor M2 during a period when the
threshold voltage information of the second transistor M2 is
sensed.
To this end, the compensation unit 142 is coupled to a voltage
source Vsus, a control line CLn, a scan line Sn, and an emission
control line En. The voltage of the voltage source Vsus may vary so
that the deterioration of the organic light emitting diode OLED can
be compensated. For example, the voltage of the voltage source Vsus
may be higher or lower than the anode voltage Voled of the organic
light emitting diode OLED. Here, the voltage of the anode electrode
Voled of the organic light emitting diode OLED, which is the
voltage shown on the anode electrode of the organic light emitting
diode OLED, varies in accordance with the deterioration of the
organic light emitting diode OLED.
FIG. 4 is a schematic circuit diagram showing an exemplary
embodiment of the compensation unit of FIG. 3.
Referring to FIG. 4, the compensation unit 142 includes a fourth
transistor M4 and a fifth transistor M5 that are coupled between
the anode electrode of the organic light emitting diode OLED and
the m.sup.th data line Dm. A third transistor M3 is coupled between
a first node N1 and the voltage source Vsus, the first node N1
being a common node between the fourth transistor M4 and the fifth
transistor M5. A feedback capacitor Cfb is coupled between the
first node N1 and the gate electrode of the second transistor
M2.
The fourth transistor M4 is positioned between the first node N1
and the anode electrode of the organic light emitting diode OLED,
and is controlled by the scan signal on the scan line Sn.
The fifth transistor M5 is positioned between the first node N1 and
the data line Dm, and is controlled by the control signal on the
control line CLn.
The third transistor M3 is positioned between the first node N1 and
the voltage source Vsus, and is controlled by the emission control
signal on the emission control line En.
The feedback capacitor Cfb transfers the voltage variation of the
first node N1 to the gate electrode of the second transistor
M2.
In the compensation unit 142 described above, the fourth transistor
M4 and the fifth transistor M5 simultaneously or concurrently
maintain a turn-on state during a period when the threshold voltage
of the second transistor M2 is sensed. The fourth transistor M4 and
the fifth transistor M5 compensate for the deterioration of the
organic light emitting diode OLED, while being alternately turned
on and turned off during a period when they are normally driven
(that is, a period when a predetermined image is displayed). The
detailed explanation of the driving thereof will be described later
in more detail.
FIG. 5 is a schematic block diagram showing an exemplary embodiment
of the switching unit 170, the sensing unit 180, and the control
block 190 of FIG. 2. For convenience of explanation, FIG. 5 will
show an embodiment where they are coupled to an m.sup.th data line
Dm.
Referring to FIG. 5, two switching elements SW1 and SW2 are
provided, that is, one on each channel of the switching unit 170. A
current sink unit 181 and an analog-digital converter (hereinafter,
referred to as "ADC") 182 are provided on each channel of the
sensing unit 180. (Here, one ADC may be provided for each of a
plurality of channels, or a plurality of channels, or all channels,
may share one ADC.) The control block 190 further includes a memory
191 and a control unit 192.
The first switching element SW1 is positioned between the data
driver 120 and the data line Dm. The first switching element SW1 is
turned on when the data signal is supplied from the data driver
120. In other words, the switching element SW1 maintains a turn-on
state during a period when the organic light emitting display
device displays an image (e.g., a predetermined image).
The second switching element SW2 is positioned between the current
sink unit 181 and the data line Dm. The second switching element
SW2 maintains a turn-on state during a period when the threshold
voltage/mobility information of the second transistor M2 is
sensed.
The current sink unit 181 sinks a first current from the pixel 140
when the second switching element SW2 is turned on (e.g., closed),
and supplies a voltage (e.g., a predetermined voltage) generated
from the data line Dm when the first current is sunken from the
pixel 140 to the ADC 182. Here, the first current is sunken via the
second transistor M2 included in the pixel 140. Therefore, the
voltage (e.g., the predetermined voltage or a first voltage) of the
data line Dm generated by the current sink unit 181 corresponds to
the threshold voltage/mobility information of the second transistor
M2. In addition, the first current varies so that the first voltage
can be applied, e.g., within a predetermined time. For example, the
first current may have a value that flows to the organic light
emitting diode OWED when the pixel 140 emits light at a maximum
brightness.
The ADC 182 converts a value of the first current sunken into the
current sink unit 181 into a first digital value.
The control block 190 includes a memory 191 and a control unit
192.
The memory 191 stores the first digital value supplied from the ADC
182. In some embodiments, the memory 191 stores the threshold
voltage/mobility information of the respective second transistors
M2 of all the pixels 140 included in the display region 130.
The control unit 192 transfers the first digital value stored in
the memory 191 to the timing controller 150. Here, the control unit
192 transfers the first digital value to the timing controller 150,
the first digital value being extracted from the pixel 140 to which
a first data Data1, which is currently input to the timing
controller 150, is to be supplied.
The timing controller 150 receives the first data Data1 from the
external source, and receives the first digital value from the
control unit 192. The timing controller 150 supplied with the first
digital value generates second data Data2 by converting the bit
value of the first data Data1 so that the threshold
voltage/mobility of the second transistor M2 included in the pixel
140 can be compensated.
The data driver 120 generates the data signal utilizing the second
data Data2 and supplies the generated data signal to the pixel
140.
FIG. 6 is a schematic block diagram showing an exemplary embodiment
of a data driver.
Referring to FIG. 6, the data driver includes a shift register unit
121, a sampling latch unit 122, a holding latch unit 123, a signal
generation unit 124, and a buffer unit 125.
The shift register unit 121 receives a source start pulse SSP and a
source shift clock SSC from the timing controller 150. The shift
register unit 121 supplied with the source shift clock SSC and the
source start pulse SSP sequentially generates m sampling signals,
while shifting the source start pulse SSP once per period of the
source shift clock SSC. To this end, the shift register unit 121
includes m shift registers 1211 to 121m.
The sampling latch unit 122 sequentially stores the second data
Data2 in response to the sampling signal supplied sequentially from
the shift register unit 121. To this end, the sampling latch unit
122 includes m sampling latches 1221 to 122m in order to store m
second data Data2.
The holding latch unit 123 receives a source output enable SOE
signal from the timing controller 150. The holding latch unit 123
supplied with the source output enable SOE signal receives and
stores the second data Data2 from the sampling latch unit 122. In
addition, the holding latch unit 123 supplies the second data Data2
stored in itself to the signal generation unit 124. To this end,
the holding latch unit 123 includes m holding latches 1231 to
123m.
The signal generation unit 124 receives the second data Data2 from
the holding latch unit 123, and generates m data signals
corresponding to the received second data Data2. To this end, the
signal generation unit 124 includes m digital-analog converters
(hereinafter, referred to as "DAC") 1241 to 124m. In other words,
the signal generation unit 124 generates m data signals using DACs
1241 to 124m positioned at each channel, and supplies the generated
data signals to the buffer unit 125.
The buffer unit 125 supplies the m data signals supplied from the
signal generation unit 124 to m data lines D1 to Dm, respectively.
To this end, the buffer unit 125 includes m buffers 1251 to
125m.
FIG. 7 is a schematic block diagram further showing a driving
waveform supplied during a compensation period of the threshold
voltage, during which the threshold voltage of a driving transistor
is compensated.
Referring to FIG. 7, the scan driver 110 sequentially supplies the
scan signals (e.g., having a low voltage) to the scan lines S1 to
Sn during the compensation period of the threshold voltage. Also,
the control line driver 160 sequentially supplies the control
signals (e.g., having a low voltage) to the control lines CL1 to
CLn substantially in synchronization with the scan signals. In this
case, the control signal on a k.sup.th control line CLk overlaps
with the scan signal on a k.sup.th scan line Sk.
During the compensation period of the threshold voltage, the
emission control signals (e.g., having a high voltage) are on a
plurality (e.g., all) of the emission control lines C1 to En so
that the third transistors M3 included in each of the pixels 140
maintain a turn-off state. In addition, during the compensation
period of the threshold voltage, the second switching element SW2
maintains a turn-on state.
Specifically describing the operation process of an exemplary
embodiment, when the scan signal first appears on the n.sup.th scan
line Sn, the first transistor M1 and the fourth transistor M4 are
turned on. When the first transistor M1 is turned on, the gate
electrode of the second transistor M2 is coupled (e.g.,
conductively coupled) to the data line Dm. If the fourth transistor
M4 is turned on, the first node N1 is coupled (e.g., conductively
coupled) to the second electrode of the second transistor M2.
The fifth transistor M5 is turned on by the control signal supplied
to the control line CLn in synchronization with the scan signal.
When the fifth transistor M5 is turned on, the first node N1 is
coupled (e.g., conductively coupled) to the data line Dm.
Here, the current sink unit 181 sinks the first current from the
first power supply ELVDD via the second switching element SW2, the
fifth transistor M5, the fourth transistor M4, and the second
transistor M2. When the first current is sunken in the current sink
unit 181, the first voltage is applied to the data line Dm. Here,
because the first current is sunken via the second transistor M2,
the threshold voltage/mobility information of the second transistor
M2 is included in the first voltage (in some embodiments, the
voltage applied to the gate electrode of the second transistor M2
is used as the first voltage.)
The first voltage applied to the data line Dm is converted into the
first digital value in the ADC 182 to be supplied to the memory
191, and accordingly, the first digital value is stored in the
memory 191. Through the above-described process, in some
embodiments, the first digital value including the threshold
voltage/mobility information of the second transistors M2 included
in all the pixels 140 is stored in the memory 191.
In an exemplary embodiment, the process of sensing the threshold
voltage/mobility of the second transistor M2 is performed at least
once before the organic light emitting display device is used. For
example, before the organic light emitting display device is
released from the manufacturer, the threshold voltage/mobility of
the second transistor M2 may be sensed to be stored in the memory
191. Also, the process of sensing the threshold voltage/mobility of
the second transistor M2 may also be performed at a time designated
by a user.
FIG. 8 is a schematic block diagram further showing a driving
waveform supplied during a normal driving period.
Referring to FIG. 8, during a normal driving period, the scan
driver 110 sequentially supplies the scan signals to the scan lines
S1 to Sn, and sequentially supplies the emission control signals to
the emission control lines E1 to En. Here, the emission control
signal on a k.sup.th emission control line Ek overlaps with the
scan signal on a k.sup.th scan line Sk, wherein the emission
control signal has a wider width than the scan signal. During the
normal driving period, the control signals are not supplied to all
the control lines CL1 to CLn (e.g., having a high voltage).
Further, during the normal driving period, the first switching
element SW1 maintains a turn-on state.
Specifically describing the operation process of an exemplary
embodiment, when first being supplied to the pixel 140 coupled to
the data line Dm and the scan line Sn, the first data Data1 is
supplied to the timing controller 150. Here, the control unit 192
supplies the first digital value extracted from the pixel 140
coupled to the data line Dm and the scan line Sn to the timing
controller 150.
The timing controller 150 supplied with the first digital value
generates the second data Data2 by converting the bit value of the
first data Data1. Here, the second data Data2 is such that the
threshold voltage/mobility of the second transistor M2 can be
compensated.
In an exemplary embodiment, when the first data Data1 having a
binary value of "00001110" is input, the timing controller 150
generates the second data Data2 having a binary value of
"000011110" to compensate for the deviation of the threshold
voltage/mobility of the second transistor M2.
The second data Data2 generated by the timing controller 150 is
supplied to the DAC 124m via the sampling latch 122m and the
holding latch 123m. The DAC 124m thereafter generates the data
signal using the second data Data2, and supplies the generated data
signal to the data line Dm via the buffer 125m.
When first transistor M1 and the fourth transistor M4 maintain a
turn-on state in accordance with the scan signal supplied to the
scan line Sn, the data signal is supplied to the data line Dm.
Here, the third transistor M3 is turned off in accordance with the
emission control signal supplied to the emission control line
En.
When the first transistor M1 is turned on, the data signal supplied
from the data line Dm is supplied to the gate electrode of the
second transistor M2. Thus, the storage capacitor Cst is charged
with a voltage corresponding to the data signal. The fourth
transistor M4 maintains a turn-on state during a period when the
storage capacitor Cst is charged with a voltage (e.g., a
predetermined voltage) so that the first node N1 receives the anode
voltage Voled of the organic light emitting diode OLED.
After the storage capacitor Cst is charged with the voltage (e.g.,
the predetermined voltage), the supply of the scan signal to the
scan line Sn stops. When the supply of the scan signal to the scan
line Sn stops, the first transistor M1 and the fourth transistor M4
turn off.
Thereafter, the supply of the emission control signal to the
emission control line En stops and the third transistor M3 turns
on. When the third transistor M3 turns on, the voltage of the first
node N1 becomes the voltage of the voltage source Vsus. For
example, when the voltage of the voltage source Vsus is higher than
the anode voltage Voled, the voltage of the first node N1 rises
from the anode voltage Voled to the voltage of the voltage source
Vsus. Here, the voltage of the gate electrode of the second
transistor M2 also rises corresponding to the voltage of the first
node N1. In this embodiment, the voltage of the voltage source Vsus
is lower than that of the first power supply ELVDD so that the
pixel displays a sufficient brightness.
Thereafter, the second transistor M2 supplies the current
corresponding to the voltage applied to the gate electrode of the
second transistor M2 from the first power supply ELVDD to the
second power supply ELVSS via the organic light emitting diode
OLED. Then, light (e.g., a predetermined amount of light)
corresponding to the amount of current is generated by the organic
light emitting diode OLED.
The organic light emitting diode OLED deteriorates as time elapses.
Here, as the organic light emitting diode OLED deteriorates, the
anode voltage Voled of the organic light emitting diode OLED rises.
In other words, as the organic light emitting diode OLED
deteriorates, the resistance of the organic light emitting diode
OLED increases, and, accordingly, the anode voltage Voled of the
organic light emitting diode OLED rises.
As the organic light emitting diode OLED deteriorates, the voltage
of the first node N1 is lowered. In other words, as the organic
light emitting diode OLED deteriorates, the anode voltage Voled of
the organic light emitting diode OLED that is supplied to the first
node N1 rises, and accordingly, the voltage of the first node N1 is
lower than the voltage when the organic light emitting diode is not
deteriorated.
If the voltage of the first node N1 is low, the voltage of the gate
electrode of the second transistor M2 becomes low. Accordingly, the
amount of current supplied by the second transistor M2
corresponding to the same data signal increases. In other words, in
an exemplary embodiment of the present invention, as the organic
light emitting diode OLED deteriorates, the amount of current
supplied by the second transistor M2 increases to compensate for
the deterioration of the organic light emitting diode OLED and
accordingly reduce the lowering in brightness.
When the voltage of the voltage source Vsus is lower than the anode
voltage Voled (in some embodiments, the voltage source Vsus is
substantially the same as the voltage of the second power supply
ELVSS), the voltage of the first node N1 falls from the anode
voltage Voled to the voltage of the voltage source Vsus. At this
time, the voltage of the gate electrode of the second transistor M2
also falls corresponding to the voltage of the first node N1.
As the organic light emitting diode OLED deteriorates, the anode
voltage Voted of the organic light emitting diode OLED rises. In
this case, as the organic light emitting diode OLED deteriorates,
the voltage of the first node N1 rises. In other words, as the
organic light emitting diode OLED deteriorates, the anode voltage
Voled of the organic light emitting diode OLED that is supplied to
the first node N1 rises and accordingly, the voltage of the first
node N1 is higher than the voltage when the organic light emitting
diode is not deteriorated.
If the voltage of the first node N1 is high, the voltage of the
gate electrode of the second transistor M2 becomes high. Then, the
amount of current supplied by the second transistor M2
corresponding to the same data signal increases. In other words, in
an exemplary embodiment of the present invention, as the organic
light emitting diode OLED deteriorates, the amount of current
supplied by the second transistor M2 increases to compensate for
the deterioration of the organic light emitting diode OLED and
accordingly reduce the lowering in brightness.
While the present invention has been described in connection with
certain exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims, and equivalents thereof.
* * * * *